Mercedes’ James Allison explains Valtteri Bottas’ botched pit stop

© Steve Etherington for Mercedes-Benz Grand Prix Ltd.

Mercedes Technical Director James Allison has explains Mercedes’ pit stop mistake that cost Valtteri Bottas more than 10 seconds at the Bahrain Grand Prix.

Before the infamous pit stop Bottas was able to follow Lewis Hamilton and Max Verstappen relatively closely, but that all changed when he was called into the pits. In Mercedes’ post-race debrief James Allison explains what went wrong.

“When the car came into the pit stop box, Valtteri came in very neatly and positioned the car neatly,” said Allison.

“Which is always a help for the pit crew, but sadly one of the gun men went onto the wheel, started to disengage the nut, loosened the nut but then started to withdraw the wheel gun just a little bit too soon before the nut had spun off its thread.

“Because it was still offering some resistance at that point, as he withdrew the wheel gun, the socket on the wheel gun started to disengage from the nut and then started to spin round.


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“We call it machining the nut because it starts to chip away at the edges of the nut and destroy the nut, a bit like when you are using a screwdriver and you don’t have it lined up properly, and you start to sort of damage the screwdriver slot.

“So, as he pulled away the gun machined away at the nut and it didn’t actually come off its mountings.

“He went back in to deal with it, but the gun recognises or is designed to recognise when it has done a gunning off action and it automatically shuttles the gun so that it is then in doing up mode.

“So when he went back on to finish the job of taking the wheel nut off, the gun is now in doing up mode and instead of undoing the nut, it is doing it up again and the subsequent sort of follow on mess of that is what causes something which is normally a beautiful two-second pit stop, causes it to then collapse into something that haemorrhages lap time and seconds in the pit lane.

“But all of it was caused by that initial misplacing of the wheel gun, machining the nut as the wheel gun came off,” concluded the Briton.

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